


Simple Math

by AikoIsari



Series: The Legacy of Great Intention [8]
Category: Digimon - All Media Types, Digimon Adventure, Digimon Adventure V-Tamer 01, Digimon Story Series | Digimon World Series, Digimon World Series
Genre: Action/Adventure, Alternate Universe - Canon Divergence, BAMFs, Canon-Typical Violence, Crossovers & Fandom Fusions, Epic Friendship, Friendship, Gen, Gods, Magic, Non-Graphic Violence, Team Bonding, Team as Family, world building
Language: English
Status: In-Progress
Published: 2017-08-10
Updated: 2018-08-14
Packaged: 2018-12-13 14:25:37
Rating: Teen And Up Audiences
Warnings: Major Character Death
Chapters: 2
Words: 4,563
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/11761818
Author URL: https://archiveofourown.org/users/AikoIsari/pseuds/AikoIsari
Summary: You take a Hikari who gets on a bus that she shouldn't. You subtract a Taichi fraction when they wake up in a strange world and she ends up with his clone. You subtract a demon and add a cult. Then you run a certain cat and bat through a variable sequence. What do you equal out to? Let's find out.





	1. Apple Flavored Cough Drops

Everyone said when you were coughing really badly, long after the sneezing and sniffling part of the deal, you weren't contagious anymore. You just looked it because everyone relied on how you looked.

Little Yagami Hikari hoped that was true because she looked  _awful_. In fact, right now, she looked so under the weather that she was allowed to take a hot morning shower after the one from last night and no one was normally allowed to do that. (If everyone did it it would be much too expensive.) She rubbed her drooping eyes in the mirror as the steam wafted through the room.

"Mrrmmmm," she grumbled as she got into the shower. Hikari wanted to bow out now. It really did feel like a mucus monster had made its home in her stomach and was trying to get lower. Gross. Her big brother would be relieved if she stayed home, him and their parents both.

Yet the very thought made her stomach hurt, quite a lot actually. So she forced herself under the spray and sighed in immediate relief.

 _I can breathe again,_ she thought to herself before letting out another ear splitting cough. Taichi's voice filtered through the door in concern. She called back that she was fine. Which she wasn't and being the big brother that he was he likely knew that. But she didn't care this time! She was going to go. And she wasn't going to stop until the answers came to her.

 _Onii-chan doesn't remember…_  And nobody believed her, but it was not a dream. Koromon had never been a dream. She looked at her tiny hands. She could see the nicks on her palms, old and long healed but still there. And when she went outside and looked at the television, she would see snow falling in summer or the flood of another desert with the monsters wavering in and out before her. She would watch statistics go up until there was an abrupt channel change, because her parents were afraid of her seeing it.

She loved them so much it hurt. But they just didn't understand.

She wasn't sure there was much point in trying to.

Hikari coughed and the mucus left her mouth and hit the floor of the tub and slid into the drain. She grimaced in disgust. Her brother would think it was cool. Sometimes Taichi could be just… silly.

Still, if it meant not coughing through the entirety of her camping trip she would take it.

Outside, her brother sifted through their bags, carefully slipping a bottle of cold medicine between a bag of snacks and his sister's teddy bear. With any luck, she wouldn't notice.

Taichi turned back to his own bag, grinning to himself. Sure, he was worried of his sister being stuck doing real rough camping for a week with a summer cold (that had seriously come from nowhere, what was wrong with her immune system?) But there was no real way of stopping her. She was a Yagami and Yagami took stubborn to a level unseen by most of the human population. He would just have to keep an eye on her and have fun.

So she wouldn't notice of course. His sister was perceptive.

* * *

Per her master's will, Plotmon continued her travels. The awkwardly angled sack of books dropped over both sides of her Holy Ring, the data inside threatening to seep into her fur and dye it black. That was the only reason she was able to carry it. If it weren't for the mysterious ring being her collar, the books would eat her alive.

That crazy guy did this on purpose she knew. It was to have proof she would be a loyal soldier, a powerful one. One that survived the power rush that came to be from being around forbidden materials would be able to serve him properly.

Honestly, Plotmon wasn't even sure she wanted to. But where could she have run? There was no one looking for her, even if she was looking for them. She didn't quite remember why she was looking but it was necessary to continue. To continue meant she had to live long enough.

She frowned to herself and kept walking.

Where was she even going anyway? She couldn't even remember through the

_-Twinge-_

Pain.

She stopped and collapsed under a tree. The bags dug into her back once more and with an irritated huff, she threw them over her head and let them smack into the opposite tree. Plotmon sagged with relief back into the grass and shut her eyes.

Stupid old vampire. Stupid books. She just wanted to find what she was looking for, not cart weird materials across a continent! Her eyes watered, full and thick globs of mucus streaming down. She stubbornly wiped them away with her paw and winced at the sting it did to the angry red mark there. She couldn't let him see her weak. That stupid master… he would laugh about it very softly, right behind her ears until the sound grew to echo into the skin beneath her fur and then trickled off. Until her guard dropped. Until she thought it was over.

Plotmon doubted that vampire could grow tired, truly. Only hibernate.

She didn't feel like getting up so she didn't. But because she didn't move. Someone moved towards her instead.

* * *

Chains rattled from where they gouged the cavern walls. Their weight rocked and strained from their source, a single flat circle that spun overhead. Well, it was more than that. Its creator could attest to such a thing.

Not that the little girl was proud of her work. There was nothing to be proud of when looking at a seal, only the expectation that it would continue to work. Because what was on the other side, as far as she was concerned, needed to bloody well  _stay there._

The little girl regarded the lines, then raised her hand, palm down, rough nib nails dripping with purple energy. She exhaled softly.

Being a goddess was only fun some of the time, really.

"Numerous lights in the heavens," she intoned, monotone dripping into the cavern walls. "Triad moons hidden behind the sun, cleanse the light. Make your darkness a beacon."

_-Reinforcement-._

The word made the air tremble and the circle shrieked its fury and rattled the chains once more. Its tendrils lashed, missing the small girl by miles. She responded to none of it, as she was taught.

Hate. The word was thunder. Wrath, pain, you pay burn-

Shrieks filled the space from mouths and metal.

The girl watched the tendrils slip through and beyond her. Her eyes widened ever so slightly. Then they returned to their normal size, as if her interest had been swallowed by food.

"Not a chance, ya codger," she said in a grunt and turned away. "I'm long ahead of you."

She just had to believe that  _being ahead_  still meant something in the long game. For now, it was back to the village. She had adventures to start.

Mikagura Mirei couldn't help the mischievous smile straining her cheeks at the thought.

* * *

_The king walks the earth without a crown._

_The ruler holds court without a sigil._

_Reality waits for no one to see it._

_But magic dances in every open palm,_

_If only they came to grasp it._

Hikari rubbed her eyes as the Yagami car pulled to a stop. She sniffled and gave her nose a hefty blow so hard she swore she felt a blood vessel explode. Finding no evidence of the sort, she tossed the tissue into the garbage and shuffled out of the car.

She regretted that in an instant. Their school wasn't small, so six classes worth of kids, plus a few stragglers from other grades or schools with permission slips, swarmed in groups and chattered loud enough to bring back the pulsing headache from the night before. Hikari nearly turned around-

Then her brother's hands, gloved as always these days, rested palms down over her ears, muffling everything with sweet relief. Hikari exhaled and beamed up at her big brother.

"All fine?" She saw his brown eyes glitter with concern and nodded.

"Let's fly, Mr. Pilot!" She chirped, red gaze locked at his goggles. Taichi's smirk widened and he picked her up to put on his shoulders.

"Taichi, be careful!" they heard their mom say. Taichi immediately began to wilt, but Hikari latched on her hands to his hair in defiance.

"This is not Taichi!" She declared in too much joy. "This is my plane to camp and we're going to take off!"

She felt the eyes on them both and didn't care. She felt the flush on her brother's face and revelled in it. She squinted at them all, daring them to comment and care. They did not understand. The ways their lips curled and they looked like pity. Looked like disdain and fear and other things. But that was only her interpretation. It could be that they found this quite cute. But it didn't matter what they thought.

This was for Taichi and his big, kind heart.

He took a grip on her calves and raced towards the bus, making the sounds of an old propeller and echoing Hikari's shrieks of glee. Not even coughing could make it not worth it, especially when their father pinwheeled her back to the ground, making her giggle. Everything felt like the warmth of her morning shower. Then her father's arms trembled and she took her bag. She managed a more new, tremulous smile.

"See you when we get back." Taichi kept his voice as calm as possible. "We'll be safe, promise."

Hikari winced at the water in their mother's eyes, then squeaked at her father hugging them both.

"Have fun."

Hikari smiled. "We will!"

With that, they were boarding the bus. Hikari made a beeline for the back. It was usually the most fun there and then she wouldn't get snot over a lot of people in the middle and the front would likely have all the teachers. She didn't need that level of fussing.

There were a couple people in the back already, from what she could see. As she passed others they whispered, "A kid went missing from my apartment last night."

"Another one?" The other girl practically whimpered, clasping her hands together. "They keep just vanishing! It's weird!"

"My dad says it's the government," said the first girl.

A boy behind her scoffed. "He  _always_ thinks it's the government."

"Well  _your mom_ said it was demons. So there"

"What's wrong with that?"

Hikari kept walking. It was likely they were all wrong. Her fingers curled up as her mind conjured images of shattered vending machines, fireballs shattering balconies… a collapsing bridge right-

She shut her eyes, breathed sharply, and then made it to an open seat. For a moment, it was all Hikari could do to breathe, her throat closing up with snot (and fear, if she was going to be honest, which she wasn't).

Then a high voice piped up. "Are you okay?"

Hikari made herself turn her head to see who she sat beside, a blond boy about the same size as her with big, concerned blue eyes. She squeaked with surprise.

"I'm sorry!" she was very lucky she was gripping the chair. "I-" She swallowed. "I'm fine. I didn't mean to disturb you." Her cheeks flamed with embarrassment. "I'm just getting over a cold, that's all."

"Ooh!" He smiled. "And you decided to come to camp anyway! That's awesome!" He dipped his head. "I'm Takaishi Takeru!"

Hikari felt herself relax. He hadn't even asked if she was contagious. Maybe this would be all right. "I'm Yagami Hikari. Nice to meet you."

"Un!" For a few minutes the two of them sat there watching people go by. Then Takeru asked. "Was that your big brother running around with you earlier?"

Hikari bit her lip, then nodded. "Uh-huh! Our parents were nervous about us coming along, but we wanted to show them it was okay."

Takeru nodded slowly, jerking in his seat as the bus started to roll away. HIkari didn't see her parents, but she could see her brother's hair shifting around as he waved at them. Close enough, she figured. "My brother wouldn't do that. He's too shy!"

Hikari tilted her head. "Your brother's here too?"

"Yep!" Takeru pointed. "Up there, with the turtleneck! Well, the half a turtleneck." She leaned up in the chair to see darker blond hair ducking out of sight, hiding in the seat. Well, he did seem kinda shy acting like that. She sat back in her chair and they listened to the teachers together. Her brother was in her group at least. That was good.

Maybe her feelings were wrong. Maybe this would just be a normal, brand new experience for her and she would just make some new friends.

Then a horrible chill ran down her spine. The ground creaked underneath the wheels. She gripped her seatbelt.

Someone in front of them let out a scream. Hikari almost shut her eyes and looked away, but then a horrible heat washed over the windows. She turned and just as she lifted her head, what could only be a miniature sun slammed into the bus and its occupants.

The stars were falling on them. Inevitably, it would crash into their tiny bus and kill them all. She was absolutely certain of this. And yet she found the energy to sneeze and cough as it came closer. Her mind rejected it however. No, that wasn't accurate. Her heart rejected this event.

And what the light rejected could only be  _scoured._


	2. The Weight of the Sun

**Notes for the Chapter:**

> Warnings: Gods, devotion, blue and orange morality, violence, blood, and fire. And if you have not read "the nights that never die", go read it I beg of you, it brings you context!

"This isn't good."

Mirei made a face of mild displeasure. Complete displeasure and anger would only give the person causing these problems the satisfaction and her more stress and she was far too young for such things.

… Okay she was actually pretty old, but for her  _species_ , she was still young enough. And for her position she was a speck. So whatever. It counted.

Mirei looked upon the might of the human world being crushed and did not despair. She only closed her eyes and reached out to it, feeling more internally than externally. Her body thrummed as she took in the scene before her.

Namely, the sun-worthy fireball that was preparing to sink down on a bus really. And a truck or two, and a heck of a lot of trees. She breathed out once, facing forward. And she  _reached_  with a power beyond her fingers and into the sky and called out,

"Yagami, do you want to live or not?"

It was a simple sentence with a simple purpose and to be honest, she had no idea if it would work. But considering who she was calling either it was going to work or she was going to have to replace an entire team of kids in like: ten human world minutes and that was a tragedy. Or was it a statistic? She really wasn't sure she wanted to know the answer.

"Do you two want to live or not?" she repeated to the air, knowing they could hear because they were old enough at this point and their father was acting like keeping destiny on course was more important now than later (the kid was too stupid to play the long game, he just  _was_ , there were older and better players than a jumped up little boy who missed his mother.) "You've got to do something, if you do, Taichi, Hikari."

Her friends were just. So. Silly. Why wouldn't they use their power to live? To keep their cover? How ridiculous.

* * *

Hikari was used to heat. Her brother's body glowed with it constantly. It bubbled under his fingertips, sometimes accidentally singing his clothes or his soccer ball or once in a while other people. But this was on an entirely other level that didn't respond to fire extinguishers and being buried in sand.

And she still could not stop sneezing. It was getting terribly inconvenient especially considering everyone around them was likely going to die. And she just couldn't let that happen.

She could hear her parents now. She could hear them telling her, you can't save everyone, you're sick, you can barely save yourself, you're too young. But she'd just made a friend and he didn't deserve to turn into human chips without dip. No one really deserved that.

So, as casually as she could, she moved from her seat. She coughed a couple of times, of course, but no one had moved yet, either absorbed by the state of the bus or having just seen the very large light in the sky and not known what it was yet. (Or she had accidentally slipped out of time, she knew someone had done that at least once.) No one except Taichi. She was surprised to realize he hadn't taken the window seat as he usually did. But now he was getting up and moving towards her with bigger steps.

"We could run," he said, a grin beginning to form on his face, all bright and bloody and cold. "Or we could fight. What are you in for?"

FIght the sun. Fight the  _sun_. Only her brother. Only her big brother.

" _Do you want to live or not?"_  registered so clearly in her ears it hurt a bit. Hikari smiled a little. Trust another to be willing to help.

Hikari took a deep breath and was so happy it came out correctly without snot and spit. "Let's fight a sun."

He grinned and strapped his goggles on.

To be precise, they weren't going to be really fighting. Just delaying, holding back while the bus crash landed.

In another world, but who needed specifics?

Neither of them were remotely capable of yanking things out of time and space but their uncle was. They just needed to cause enough of a fuss to get his attention.

The world trembled and time caught up to them. People were starting to scream. She saw Taichi's left eye twitch and tried very hard not to smile. Her brother was kind but he was also very impatient. She could hear him thinking  _humans._ He was  _so_  like dad.

"Stop the bus," he shouted and raced towards the front with her in his arms anyway. She really hoped he didn't just bust through the windshield with her in tow, them surviving that would be difficult to explain. Then again so was what they were about to do but they could always lie about that. Human brains quickly made up excuses a lot of the time

After all, she had had a feeling that she'd absolutely needed to be on this bus today. Now she knew why.

Some old god was dropping a sun on some children. Not cool.

Thankfully the bus screeched to a halt instead, leaving the door to rush open in the middle of the highway. Everyone else was stopping which made it all too easy for Taichi to run out with her and then, without hesitation or subtlety, climb to the top of the bus.

Meanwhile, Hikari was coughing, hard. She spat on the ground and groaned. "Colds are  _gross_." She really hated her immune system right now. Why did she even get sick?

He set her down, patting her shoulder. "Don't worry, we'll probably pass out super hard when this is over so you'll get to sleep it off. Get on it quick or else."

Hikari shot her brother a scowl. He was  _so_  buying her ice cream later. Then she looked away from his wry grin and focused on his eyes. His eyes were narrowed in concentration, a vivid clear  _blue_  in place of his normal soft brown. She sneezed and picked herself up fully. Her eyes were furiously closed, the heat still a mild tickle on her face.

Then, inexplicably, the air let out a  _thud._

Or perhaps the wind was knocked out of itself. No matter. The air met the force of the meteor (which now that Hikari could kind of see, it wasn't the sun, just a meteor which wasn't much better but it was much less terrifying) as it dove down and down.

Her brother started to sweat. "She makes this seem so easy."

"She's also  _actually_  a god, Nii-chan."

"Don't get smart with me."

Ooh she was going to  _get_  him for that one.

Someone was shouting behind them. Loudly. What was it? Something about coming back inside? No, outside, something outside, something else was-

Something else was falling. And it was faster.

"Nii-chan?"

"They're smaller," he said, which asn't that helpful considering her eyes were shut. "I mean, they're like the size of chicken eggs."

"Oh."

That was about as far as either of them got before both of them were smacked in the gut with one each. Tai crumpled to the roof of the bus as the meteors punctured holes into the poor stuck vehicle. People screamed of course.

"Ow," Hikari managed to say, sitting up. Her brother didn't say anything at all and she looked to see the device pulsing with a steady, orange light around him. She uncurled her hands around from where she had wrapped around her own and it glowed a steady, warm pink. She clapped her hands around the thing and it didn't stop glowing. Great.

Maybe she could use it. She pulled one hand away, which was harder than she thought it would be, and made to shake her brother away. Taichi didn't stir.

Despite the heat getting steadily warmer and closer, Hikari pouted.

"I gotta do all the hard work myself," she told him. This of course didn't get him to wake up any faster.

So she turned to look death in the face and dug. Dug into her heart, dug into the place beneath the human body's pains and ills to what everyone said connected people to the world.

 _"I named you for the lights of the world,"_  her mother had said one day, pretending to be a mystical sort, or at least more mystical she was when she wasn't cooking outside of the recipe.  _"Your brother for the first, you for the many lights. And I was right to do it."_

Trite, probably, not useful, if her friends were anything to go by. But now she had to believe it with all of her heart. She was named for the light, and now she had to  _become it._

Something shrieked in the sky, possibly with laughter. Daring her to try, waiting for her to fail.

Hikari looked at the sun and did not blink. If she was going to blind herself to save these people then so be it  _she would._

"Help me," she uttered. She cast her hand out to the sky, the strange meteor pulsing in it. "You called to me, you asked me, now  _help me help them."_

And the air  _thrummed_ in answer. There was a trilling sound and it echoed in her bones. She couldn't see, but she didn't need to. Hikari took a step away from her brother, and another, and another, until she was no longer stepping on anything at all. Or perhaps there was the air, or the trees, or the cars and trucks and buses using this lonely road that led to ports and camp sites. She could be flying for all she knew. Hikari couldn't be bothered to care.

"Help me," she uttered again. "I don't want to die! Do you?"

And seven lights answered, wrapping around, wrapping and pulsing about as the world responded that  _no, it did not._

And then the heat, concentrated before her face, kilometers from her nose, exploded.

Hikari fell and as she fell she thought she heard her father say,  _what am I going to_ do  _with you two?_

But he wasn't here, so that couldn't be right.

As blissful unconsciousness dragged her down, she could have sworn she heard someone giggle.

* * *

Takenouchi Sora woke up to the world on fire.

Or a world on fire. Japan, last time she paid attention in science class, didn't have burning palm trees. Or rough hard earth, or blue leaves on anything.

Maybe it was manufactured, maybe that didn't matter because there was still fire everywhere. There were people crying, the sound of grunts in moving bodies, so much to do so much was wrong and-

She coughed smoke and groped around. Her fingers closed around something small and cool, cold even through the leather. Her heartbeat slowed, calmed. The screaming didn't mute, but it softened, went down easier.

"Sora!"

The voice cut through her calm and she opened her eyes. There was a boy stumbling with a smaller one on his back, a blond boy desperately tugging on something moving alongside his bag. And ahead of them all was Taichi, but Taichi hadn't been wearing a yellow cape when he'd run outside of the bus. Still, he gestured for her.

"Come on," he said. "We've gotta hurry so we can put the fire out and get everyone else."

That made no sense. But maybe this was a dream, where things didn't have to makes sense. She went, stepping over bodies and people. She saw a piece of fabric, pink and dangling. Someone was crying.

Realistically, though, who wasn't crying?

Everything smelled like fire.

Wasn't she supposed to be at camp? Weren't they supposed to be having fun and setting up tents? She'd wanted to get away from her mother but not-not like this?

Not forever!

Or maybe she had.

She didn't want to think about that.

She stumbled out, nearly knocking into the girl with the cowboy hat and the smaller boy clutching his laptop tight to his chest as if it would run away. His irises were barely visible, the whites so large they were like moons with veins. He breathed hard and fast and without thinking she touched his shoulder.

"It's okay, Koushiro-kun," she tried to tell him, tried to croak out some believeable lie. "We're out, we're okay."

"We are not," he said, shaking his head painfully hard. "We are not."

She couldn't reply to that.

Then water crashed into the bus, stoking out the flame as Taichi bolted back inside.

"Zero!" he called after him. "Hurry up, need your ham hands!"

"My hands aren't food, Taichi," rumbled something as a giant blue dragon dog…  _thing went_  after him and went into the bus with a mild  _squish_ of the stairs _._  And then they were carrying out people.

The girl beside Koushiro screamed. Sora was right there with her. But soon they came out with kids, and their teacher and it was that that called Sora into action.

They were injured, bleeding. Maybe they were dead, but there was no way to know, no way to tell, they had to-

"Sora!"

Another voice, much lower, by her waist. It was a giant pink bird, staring up at her with such innocent, earnest hope that it hurt.

"I found you, Sora!" The bird said with joy. It turned its whole body around. I found them, everyone! I found them!"

And as more monsters rushed to them, squeaking and shouting and enraptured, this time, Sora had to scream.

Forgotten on top of the bus, Hikari stirred.

**Notes for the Chapter:**

> Today's chapter was brought to you by my lack of patience and the sheer amount of time this chapter took from me because I rewrote the initial plan. Also the entire Digimon All Star server screaming at me about the dadgomon!AU. Ya'll are welcome. Please review me, I feed on the screams of my readers and keeping my lights on. Or commission me. Best way of contact is through tumblr or discord. Please see my site for details.

**Author's Note:**

> This took a week too long. Welcome to my last Adventure rewrite until at least next month. This is the official restart of OnixflametheBlue's Zero Hour/Legacyverse and we are starting with everyone's favorite things: Hikari from the beginning and destruction. I have mostly free reign! Be very afraid! Onix, do you have any words for the crowd?
> 
> Onix: Welcome to the ride. I'm stuck here with you. I have no idea where this is going to go despite having imput into this. For what it's worth, I'm sorry for everything.
> 
> No worries, I'm not sorry at all. So, please put your comments below in the shiny box down there. It really means a lot ot us to hear your feedback. And until next time!


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